muscle physiology

There are different components that can be trained/manipulated which contribute to maximal size. Of course there's actual myofibrillar hypertrophy (an increase in the size of the contractile fibers). There's also sarcoplasmic hypertrophy (an increase in non-contractile components of the muscle such as glycogen, water, minerals, mitochondria, etc). Capillary density can also be improved (increasing nutrient availability to muscle fibers). There are three major types of muscle fibers: Type I (or slow oxidative), Type IIa (fast oxidative/glycolytic) and Type IIx (fast glycolytic). The old Type IIb fibers turn out only to exist in animal models; IIx describes the highest threshold fibers in humans. Each fiber type has a distinctive physiology in terms of force and growth capability, fatigueability, etc. Type I fibers have the lowest force output and growth potential and take the longest to fatigue and Type II fibers have a higher force output and growth capacity and fatigue more quickly with Type IIa being intermediate between Type I and Type IIx. We might simplistically look at the rep schemes of holistic training as hitting a given pool of motor units: sets of 4-6 for Type IIx, sets of 12-15 for Type IIa and sets of 40 for Type I. This isn't necessarily incorrect although it goes a little beyond that.

Dr. Hatfield may have been one of the first Americans to latch onto the idea that there were different components of a muscle that contributed to muscle growth. This goes along with the European idea of myofibrillar vs. sarcoplasmic hypertrophy (this topic is discussed in greater detail in my UD2 book, I am the mother-f*****g PIMP). Myofibrillar hypertrophy refers to growth of the actual contractile component of the muscle fiber while sarcoplasmic hypertrophy refers to growth of everything else: glycogen, water, minerals, mitochondria and capillaries. The key thing to note is that each component requires a differential type of stress to stimulate growth.